1. Field of Invention
This invention is a fitting which effectively protects the vent openings of a carburetor from dynamic pressure caused by air currents which may exist around the carburetor. This fitting reduces the undesirable effect of this dynamic pressure on the fuel flow of the carburetor.
2. Description of Prior Art
Carburetors operate using air pressure differences acting to force fuel into a bore of the carburetor, and hence to an engine. This fuel flow is through one or more fuel metering orifices. Modern carburetors use multiple systems or circuits to provide the proper fuel/air ratio required for all engine operating parameters. These systems provide a balance between economy and power, enabling maximum power to be delivered by the engine upon demand, but maximum economy whenever possible.
Two basic elements determine the fuel flow in any of these various circuits. The first element is the physical size of the fuel metering orifice, and to a lesser extent, connecting passageways which comprise the particular fuel circuit. The metering orifice is usually sized to be considerably smaller than the other parts of the fuel delivery system, and for the purpose of analyzing fuel delivery, it can be assumed that the metering orifice constitutes the entire fuel delivery system. The second element is the pressure difference existing across the fuel delivery system, or essentially, the pressure existing across the metering orifice. For any given set of conditions, the fuel flow through the fuel delivery system varies approximately as the square root of this pressure difference.
The pressure difference acting across the fuel metering orifice, called the fuel driving pressure, in its most basic configuration consists of the pressure existing on the fuel in the fuel chamber of the carburetor, less the pressure existing in the carburetor bore where the outlet of the fuel delivery system is located, less the head pressure of the fuel, the distance the fuel must be raised from its level in the carburetor to the point at which it enters the bore. The pressure existing on the fuel in the fuel chamber is controlled by an average reference pressure established by a vent. If the vent is entirely external to the carburetor and its air induction passage, the venting is called external, and atmospheric pressure is the average reference pressure used for the carburetor. If the vent communicates with a region of the bore or other area of the air induction passage, for instance the air cleaner, this venting is called internal. In this case, the average reference pressure used for the carburetor will be slightly less than atmospheric, depending on the location of the pressure sensing end of the vent. Both types of venting, internal and external, are well known in the art.
Since the pressure internal to the carburetor, which is established by the venting system, is a factor in establishing the fuel driving pressure and hence fuel delivery rate, it is desirable to have this internal pressure maintained at a desired level, without influence by outside conditions such as wind currents.
There are two basic types of carburetors, float bowl carburetors and wet diaphragm carburetors. In a typical float bowl type carburetor, fuel flows from a larger fuel tank into the float bowl of the carburetor, the level of fuel in the float bowl being determined by a float-actuated valve. In this case, the venting system used, whether internal, external, or a combination of both, determines the pressure existing in the air occupying the space above the fuel internal to the carburetor. This pressure may contain pressure pulses due to fuel inlet valve instability or due to pressure pulses in the carburetor bore, but the average of this pressure is one parameter which determines average carburetor fuel delivery.
In a typical wet diaphragm type carburetor, fuel flows under pressure from the larger fuel tank to the carburetor, and the pressure internal to the carburetor is controlled by a diaphragm-operated valve. In this case, there is no fuel level specifically, as there is no void internal to the carburetor, it is completely filled with fuel. In this type carburetor, the dry side of the diaphragm, or the side of the diaphragm opposite the side in contact with the fuel, is housed in a chamber which is either internally or externally vented. The average pressure of this chamber, while not being the actual pressure existing on the fuel internal to the carburetor, is the average reference pressure which determines the fuel pressure internal to the carburetor. This average reference pressure exists on the dry side of the diaphragm, while the fuel pressure internal to the carburetor exists on the wet side of the diaphragm. The movement of this diaphragm positions the moveable member of an inlet valve, and hence regulates the average fuel pressure in the carburetor and therefore helps determine average carburetor fuel delivery.
Prior art has discussed how changes in internal carburetor reference pressure will change the flow of fuel to an engine. U.S. Pat. No. 1,740,917 to Beck (1926) uses an internal vent orifice in the carburetor bore which has its pressure affected by the throttle position. This internal vent, used in conjunction with a throttled bleed to the outside atmosphere, determines the internal pressure in the carburetor, thus affecting fuel flow. U.S. Pat. No. 5,021,198 to Bostelman (1990) describes a carburetor altitude compensation system using a pressure splitter to regulate the fuel flow through the carburetors. In this system, a sealed metering chamber and diaphragm is used to position a valve (choke), which changes the intermediate pressure existing between two orifices. One orifice is located in the line from the venturi region of the carburetor bore, providing a vacuum which tends to decrease the flow of fuel. The other orifice is in the line connected to a region of essentially atmospheric pressure, for instance the air cleaner. This line tends to establish the float bowl pressure at atmospheric pressure, at which maximum fuel flow will occur. The movement of the diaphragm causes a change in the relative size of the two orifices, therefore causing a change in the intermediate pressure existing between the two orifices. This intermediate pressure is applied to the carburetor and is the carburetor reference pressure, and fuel flow varies as the reference pressure varies.
In my co-pending application 08/846815, filed on Apr. 30, 1997 and now U.S. Pat. No. 5,879,595, I describe a carburetor fuel flow regulator which affects the fuel flow by varying the carburetor reference pressure. This regulator uses a moveable member which changes gas flow speed parallel to an orifice, thereby affecting the static pressure existing in the orifice, and this variable pressure determines the carburetor reference pressure and hence fuel flow. In my co-pending application 08/891433, filed on Jul. 10, 1997 and now U.S. Pat. No. 5,879,594, a temperature controlled pressure splitter is used to modify carburetor reference pressure and fuel flow.
None of the above mentioned references disclose the effect of dynamic pressure existing at the carburetor vent opening and the effect this dynamic pressure will have on carburetor fuel flow. This dynamic pressure is caused by wind currents which are likely to exist under the hood, and hence around the carburetor, of any moving vehicle.